This invention relates generally to the field of pharmacotherapeutics and the use of photodynamic therapy (xe2x80x9cPDTxe2x80x9d) to reduce or prevent inflammation due to injured tissue, whether by intestinal injury, such as surgery, or by accidental injury, such as skin lacerations, injuries to joints and tendons, and the treatment of burn victims. In a preferred embodiment, the invention relates to the use of xe2x80x9clow dosexe2x80x9d PDT to treat ocular tissue where inflammation is due to the manipulation of eye tissue, especially when the inflammation presents a complicating factor in the patient""s recovery from a necessary procedure. Common applications include inflammatory eye disease and various types of ocular surgery or laser treatment, such as transplantation and the filtration ocular surgery commonly used to treat glaucoma. In a particularly preferred embodiment, the invention relates to the extension of filtration bleb survival to improve the outcome of filtration surgery.
The four cardinal signs commonly associated with inflammation are: (1) redness, (2) swelling, (3) heat and (4) pain, with an optional fifth cardinal sign being loss of function of the affected part. While injury triggers a complex series of events, many of which occur simultaneously and are interrelated in a variety of ways, it is known that small blood vessels participate in an important way in the induction of inflammation. In fact, inflammation is one of the body""s valuable defense mechanisms and is generally thought of as having three phases: the degenerative phase, the vascular phase, and the healing phase. See Klein, xe2x80x9cDefense Reactions in Actionxe2x80x9d, Immunology, The Science of Self-Nonself Discrimination, Chapter 14, 577-84 (1982), the disclosure of which is hereby incorporated by reference.
Specifically, in the degenerative phase, the affected cells, primarily epidermal cells and fibroblasts become swollen, with their cytoplasms becoming vacuolized and their nuclei enlarging and fragmenting. Some of the platelets in the damaged blood vessels disintegrate and release serotonin and other mediators acting on sympathetic nerve endings.
The vascular phase is characterized by changes in the blood vessels, extensive migration and activity of the so-called inflammatory cells (granulocytesxe2x80x94particularly neutrophils, lymphocytes, monocytes and macrophages), and the clearing of degenerated cells and cellular debris. The capillary network and the postcapillary venules become flooded, congested and engorged by blood in active hyperemia. Because the number of capillaries also proliferate, one observes the reddish appearance of inflamed tissue, sometimes called xe2x80x9cflare.xe2x80x9d The increased blood flow also causes the temperature of the inflamed area to approach that of warmer aortic blood, as compared with the surrounding normal tissue, giving the sensation of heat.
Upon injury, the damaged tissue releases substances known to be related to histamine called H substances, which are a mixture of histamine and serotonin released by disrupted tissue mast cells. The H substances cause an active dilation of blood vessels, and the endothelial cells of the dilated vessel separate from one another, causing the gaps between them to enlarge. The endothelium lining the blood vessels gradually becomes paved with leukocytes, forcing some of the fluid out into the surrounding tissue. The protein-rich fluid that leaks out of the vessel into the surrounding tissue causes tissue swelling. The leakage of fluid also contains substances that neutralize bacterial toxins and aid in the destruction of the agent causing the inflammation.
The leukocytes, particularly neutrophils and monocytes, move about on the blood vessel wall until they find a suitable gap through which they can emigrate into the perivascular structures and tissue spaces. The leukocytes attack the dead and dying cells, digesting them intracellularly by phagocytosis or extracellularly by proteolytic enzymes released from their lysosomes when they themselves die. The stimuli for leukocyte emigration is believed to come from the injured tissue in the form of chemotactic factors.
Platelets are another cell type profoundly affected by tissue injury. Shortly after the injury, platelets, singly or in clumps, adhere to the vessel walls. Simultaneously, fibrin fibers begin to appear, forming a fine mesh that helps to trap cells. The resulting clot pulls the edges of the disrupted tissue together.
The intra- and extracellular digestion of necrotic tissue by neutrophils and monocytes produces a fluid that combines with the serous material being extruded from the blood vessels. If an abscess forms, the cavity is lined by a pyrogenic membrane that, in wounds infected with bacteria, prevents the dissemination and multiplication of pathogenic microorganisms into the blood.
In the first two phases of the inflammatory process, the foreign body is either destroyed, for example, if the foreign body is an organism, or the tissue around it is loosened, for example, if it is a splinter. In the healing phase, the inflammation begins to subside; individual blood vessels and vascular patterns become normal once again; and repair of the wound commences. The three main events in the repair process are (1) formation of new connective tissue by proliferating fibroblasts; (2) regeneration of epithelium; and (3) outgrowth of new capillaries.
Even before the inflammation subsides, fibroblasts begin moving into the injured area from the surrounding normal tissue, where they usually exist in a dormant state. They migrate by an ameboid movement along strands of fibrin and distribute themselves throughout the healing area. Once fixed into position in the injured tissue, they begin to synthesize collagen and secrete this protein, which arranges itself into fibers. The fibers orient themselves with their longitudinal axes in the direction of the greatest stress. As the collagen bundles grow in firmness, the fibroblasts gradually degenerate and attach closely to the bundles, and the injured area transforms into scar tissue.
Simultaneously with scar tissue formation, the intact epidermal cells on the edge of the wound begin to proliferate and move, as one sheet, toward the center of the injured area. As the inflammation subsides, a need for a direct supply of blood arises, and new vessels begin to grow into the wound.
It is known that, looking at inflammation on a molecular basis, a number of active compounds interact with one another in a complex manner. Among the cells damaged by injury are mast cells, which release mediators that trigger an early phase of vasodilation, accompanied by the separation of endothelial cells and exposure of collagen fibers in the subendothelial layer. Fibers in the intercellular gaps that form in blood vessels trap platelets and trigger the release of mediators from these cells.
In addition to platelets, the exposed collagen fibers also interact with proteins of the plasma that filter through the pores of the dilated vessel wall, including the triggering factor of the blood-clotting cascade. These proteins also initiate the kinin-bradykinin cascade, producing bradykinin, which becomes involved in vasodilation, the increase of blood vessel permeability, and chemotaxis.
A fourth molecular system, the complement cascade, can be activated by several stimuli: the injured blood vessels, the proteolytic enzymes released by the damaged cells, the membrane components of any participating bacteria, and antigen-antibody complexes. Some of the activated complement components act as chemotactic factors, responsible for the influx of leukocytes into the inflamed area. Others facilitate phagocytosis and participate in cell lysis.
Glaucoma is a disease of the eye in which high intraocular pressure causes damage to the individual""s vision. In a normal eye, fluid is produced by the epithelial cells of the ciliary body, which is located around the inner circumference of the iris (toward the inside of the eyeball). The functions of this fluid include nourishing the cells in the eye and keeping a positive pressure within the eyeball, which is necessary for maintaining the correct spatial distribution of the visual parts needed for image formation, similar to the supporting structure of a camera body in a photographic camera.
The fluid is normally removed from the eye by filtration through the trabecular meshwork, a circular body placed circumferentially in the angle between the iris and the cornea in the anterior portion of the eye. The fluid typically drains through microscopic holes in the trabecular meshwork into Schlemm""s canal, and then through connector channels that lead the fluid into the episcleral veins and out of the eye. In the pathology of glaucoma, the outflow of the fluid from the eye is reduced, resulting in a sharp increase in intraocular pressure, damage to the inner eye tissues and, eventually, the complete loss of vision.
The therapeutic objective in treating glaucoma is always the same, i.e., to lower the intraocular pressure, either by decreasing fluid production or by increasing the drainage or xe2x80x9cfiltrationxe2x80x9d of the fluid out of the eye. While there are many means to accomplish this objective, medication is always tried first. If medication is not successful in controlling the elevated intraocular pressure, other more invasive techniques are used, such as laser treatment or surgical intervention.
Laser procedures include trabeculoplasty, in which the laser is used to burn holes in the trabecular meshwork. Surgical techniques include (1) a trabeculotomy, which uses a metal probe or xe2x80x9ctrabeculotomxe2x80x9d to create an opening between Schlemm""s canal and the anterior chamber of the eye for roughly one third of the circumference of the normal drainage angle; (2) a trabeculectomy, which involves cutting through the trabecular meshwork; and (3) an iridectomy which refers to the cutting out of portions of the iris. A sclerostomy involves cutting through the sclera with either a laser or a surgical instrument. Trabeculectomy, iridectomy and sclerostomy are all associated with the formation of a filtration xe2x80x9cblebxe2x80x9d, a small bladder into which excess ocular fluid is shunted to expedite drainage away from the eye.
Glaucoma filtering surgery is usually recommended for patients who have progressive glaucomatous damage and those who, at their current level of ocular pressure, are at a significant risk for progression of the disease. For patients with severe damage, the long-term prognosis is improved when the intraocular pressure (xe2x80x9cIOPxe2x80x9d) can be reduced to less than 20 mm Hg and maintained below this level. Thus, in patients with advanced damage and ocular pressures above 18-20 mm Hg, filtering surgery is usually strongly recommended.
The surgery generally falls into one of two categories: (1) full thickness procedures or (2) guarded fistula procedures. The more basic, guarded fistula procedure typically involves the following trabeculectomy steps:
a. retracting the eyelid;
b. penetrating the limbus (a translucent tissue that represents the transition between the opaque sclera and the clear cornea of the eye) to produce an opening into the anterior chamber (bounded by the colored iris and the clear cornea covering the iris) from the outside of the anterior portion of the eye;
c. at a point below the iris, peeling back the outer layers of the conjunctiva and cutting a triangular scleral flap with the base of the triangle at the limbus;
d. entering the anterior chamber from the base of the triangular scleral flap;
e. excising a portion of the underlying trabecular meshwork to form a fistula, or connecting channel;
f. excising a small portion of the iris through the fistula;
g. using sutures to close the scleral flap;
h. suturing closed the conjunctiva; and
i. injecting a physiologically acceptable fluid, such as basic salt solution (xe2x80x9cBSSxe2x80x9d), into the anterior chamber through the exterior opening penetrating the limbus, which was made in step b, to elevate the bleb formed along the limbus, to confirm that the fistula is not blocked, and to confirm that there are no leaks in the bleb.
The full thickness procedure differs in that a direct opening, without the scleral flap, is created to connect the anterior chamber to the subconjunctival space through the limbus. After the outer layers of the conjunctiva have been peeled back, the fistula is created by sclerectomy (cutting a lip of tissue out of sclera at the limbus), thermal sclerostomy (cutting a shallow groove in the sclera parallel to the limbal surface), laser sclerostomy, or trephination. Stewart, xe2x80x9cFiltering Surgeryxe2x80x94Techniques and Operative Complicationsxe2x80x9d, Clinical Practice of Glaucoma, Chapter 10, 333-61 (1990), the disclosure of which is hereby incorporated by reference.
Following surgery, the condition of the filtration bleb is carefully observed on a regular basis. Initially, the bleb is usually well-elevated off from the sclera. Many eyes show a beginning area of avascularity in the conjunctiva the first day postoperative, usually around the fistula site. The avascular area is identified by noting a localized loss of capillaries and venules. However, when examining the anterior chamber, a small amount of redness or flare may be present, indicating inflammation. The IOP in the first postoperative week is usually less than 5 mm Hg, although it may be in the 6-10 mm Hg range. After the initial examination, the patient is typically started on an antibiotic-steroid combination. Stewart, xe2x80x9cPostoperative Complications of Filtering Surgeryxe2x80x9d, Clinical Practice of Glaucoma, Chapter 11, 363-90 (1990), the disclosure of which is incorporated herein by reference.
In the second to fourth postoperative week, the conjunctiva and the bleb become less inflamed, and the anterior chamber becomes xe2x80x9cquietxe2x80x9d as the amount of flare subsides. Also, as a result of scarring, the bleb usually becomes a little smaller. Additionally, the bleb generally continues to show an avascular area that may increase in size. The IOP in the second to fourth postoperative week usually rises to 10 mm Hg or above. Stewart, xe2x80x9cPostoperative Complications of Filtering Surgeryxe2x80x9d, Clinical Practice of Glaucoma, Chapter 11, 363-90 (1990).
After four weeks of an uncomplicated post-operative course, the conjunctiva usually has little or no inflammation. The well-functioning bleb typically maintains an avascular area and may either be minimally or well-elevated off the sclera. Additionally, the IOP should stabilize during this period, ideally between 10 and 15 mm Hg. Topical postoperative steroids are tapered slowly, according to the amount of inflammation in the filtering bleb and the anterior chamber. If the bleb remains vascular and inflamed, steroids are commonly maintained, and sometimes even increased, to hasten the resolution of any anterior segment inflammation, thus limiting scar formation. Stewart, xe2x80x9cPostoperative Complications of Filtering Surgeryxe2x80x9d, Clinical Practice of Glaucoma, Chapter 11, 363-90 (1990).
Unfortunately, during the early postoperative period after filtration surgery, a patient may suffer a variety of different complications, one of which is bleb failure. In many patients, bleb failure occurs between 1-6 months postoperatively, and the bleb ultimately fails to control the ocular pressure Clinically, filtering blebs that are functioning poorly are usually small in extent, are poorly elevated, and become at least partially vascularized, and the IOP again becomes elevated above the normal range. Stewart, xe2x80x9cPostoperative Complications of Filtering Surgeryxe2x80x9d, Clinical Practice of Glaucoma, Chapter 11, 363-90 (1990).
The success of filtering surgery depends upon how long after the surgery the bleb remains functional. Patients typically develop bleb failure from either a blockage at the fistula site or from scarring at the interface between the conjunctiva and the sclera. If the fistula site is blocked, one of several laser therapy techniques or conventional surgical techniques may be used. Unfortunately, however, even if the fistula is thus opened, the aqueous outflow may be limited due to previous bleb scarring to the sclera. If these procedures fail and the patient""s IOP is uncontrolled on maximal medical therapy, performing another filtering procedure at a different location may be necessary. If the fistula remains open but the bleb is small, the increased IOP probably has resulted from scarring between the conjunctiva and the sclera, which remains the most common cause of bleb failure. Stewart, xe2x80x9cPostoperative Complications of Filtering Surgeryxe2x80x9d, Clinical Practice of Glaucoma, Chapter 11, 363-90 (1990).
The manipulation of the eye tissues, especially conjunctiva, in filtering surgery necessarily causes inflammation and, eventually, scarring. In general, the more the manipulation, the shorter the bleb survival time. Because filtering surgery in patients at high risk for glaucoma often results in failure as a result of postoperative scarring, fibroblasts appear to play a critical role in this process. Katz et al, xe2x80x9cMitomycin C versus 5-Fluorouracil in High-risk Glaucoma Filtering Surgeryxe2x80x9d, Ophthalmology, 102:9, 1263-68 (1995). One of the primary reasons for failure in glaucoma filtration surgery is the presence of fibroblasts in subconjunctival tissue, (Berlin et al, xe2x80x9cThe Role of Laser Sclerostomy in Glaucoma Surgeryxe2x80x9d, Current Opinion in Ophthalmology, 6:102-114 (1995)), and when the operation fails, it is usually because there has been fibroblast proliferation and scarring at the filtration site (Mora et al., xe2x80x9cTrabeculectomy with Intraoperative Sponge 5-Fluorouracilxe2x80x9d, Ophthalmology, 103:963-70 (1996)).
In so-called xe2x80x9chigh riskxe2x80x9d patients, where there is a high percentage of bleb failures due to fibrosis, sometimes treatment concomitant with the surgery to extend the survival of the filtering bleb is helpful. Many techniques have been devised to reduce inflammation and scarring, thus prolonging the function of the filtering bleb created in filtering surgery, such as simple digital massage of the eye on a periodic basis for about four weeks following surgery.
Pharmacologic techniques to limit scarring by inhibiting the inflammatory response and preventing the formation of collagen at specific steps along its synthetic pathway have also been tried. Corticosteroids are often used, either topically as drops or injected subconjunctivally, to help prevent scarring of the bleb by inhibiting the inflammatory response and fibroblast proliferation. Stewart, xe2x80x9cFiltering Surgeryxe2x80x94Techniques and Operative Complicationsxe2x80x9d, Clinical Practice of Glaucoma, Chapter 10, 333-61 (1990). Usually, topical steroids are continued to minimize scarring until the anterior segment inflammation resolves. Stewart, xe2x80x9cPostoperative Complications of Filtering Surgeryxe2x80x9d, Clinical Practice of Glaucoma, Chapter 11, 363-90 (1990). A typical treatment program might indicate post-operative use topically every three hours with rapid tapering over 20 or so days. Araujo et al., xe2x80x9cA Ten-year Follow-up on a Prospective, Randomized Trial of Postoperative Corticosteroids after Traveculectomyxe2x80x9d, Ophthalmology, 102:1753-59 (1995).
5-Fluorouracil (xe2x80x9c5-FUxe2x80x9d) is a fluorinated pyrimidine analog with antimetabolic activity (a competitive inhibitor of thymidylate synthase), which also exerts an anti-fibrotic effect by decreasing fibroblast proliferation, thus preventing the scarring of the filtering bleb. Typically, 5-FU has been used in cases with poor surgical prognoses. At the two-year point, 5-FU has shown a success rate for filtering surgery between 60 and 70%. 5-FU is usually administered by a series of subconjunctival injections.
However, in addition to the inconvenience and discomfort of frequent and repeated postoperative injections, a number of serious complications have been reported with subconjunctival 5-FU, including epithelial defects, subepithelial scarring, corneal ulcerations, conjunctival wound leaks, bleb leaks, suprachoroidal hemorrhage, retinal detachment and endophthalmitis. Thus, although 5-FU can prolong bleb life, the incidence of corneal epithelial defects, scarring, and vascularization is also high due to the general toxicity of this agent. Stewart, xe2x80x9cFiltering Surgeryxe2x80x94Techniques and Operative Complicationsxe2x80x9d, Clinical Practice of Glaucoma, Chapter 10, 333-61 (1990). See also Khaw et al., xe2x80x9cFive-minute Treatments with Fluorouracil, Floxuridine, and Mitomycin Have Long-term Effects on Human Tenon""s Capsule Fibroblastsxe2x80x9d, Arch. Ophthalmol., 110:1150-54 (1992); Kupin et al., xe2x80x9cAdjunctive Mitomycin C in Primary Trabeculectomy in Phakic Eyesxe2x80x9d, Am. J. of Ophthalmology, 119:30-39 (1995); and Katz et al., xe2x80x9cMitomycin C versus 5-Fluorouracil in High-risk Glaucoma Filtering Surgeryxe2x80x9d, Ophthalmology, 102:9, 1263-69 (1995). See also Kay et al. xe2x80x9cDelivery of Antifibroblast Agents as Adjuncts to Filtration Surgery-Part II: Delivery of 5-Fluorouracil and Bleomycin in a Collagen Implant: Pilot Study in the Rabbitxe2x80x9d, Ophthalmic Surg., 17:796-801(1986); and Khaw et al, xe2x80x9cEffects of Inoperative 5-Fluorouracil or Mitomycin C on Glaucoma Filtration Surgery in the Rabbitxe2x80x9d, Ophthalmology, 100:367-72 (1993).
Some writers have reported that corneal edema due to inadvertent intraocular exposure could be prevented by the use of a lower concentration, e.g., 0.5 mL of 10 mg/mL 5-FU, in the usual subconjunctival injections. Chalfin et al., xe2x80x9cCorneal Endothelial Toxic Effect Secondary to Fluorouracil Needle Bleb Revisionxe2x80x9d, Arch. Ophthalmol., 113:1093-94 (1993). Others have noted that the use of 5-FU can be made safer and more effective by intraoperative administration using a sponge soaked with 50 mg/mL of the compound and leaving the sponge in contact with the bleb site for a short period of time. Mora et al., xe2x80x9cTrabeculectomy with Intraoperative Sponge 5-Fluorouracilxe2x80x9d, Ophthalmology, 103:963-970 (1996). However, even then, supplemental postoperative injections are needed in some cases, and their injections are still associated with an undesirably high incidence of corneal epithelial damage.
The deoxyribose sugar of fluorouracil, floxuridine, is about 100 times as potent as fluorouracil in long-term inhibition of ocular fibroblasts, and so can be given as a single dose. However, the difference between causing cell death, rather than inhibition, is relatively small. Therefore, the use of floxuridine is susceptible to the danger of exposing normal tissues to relatively high doses of potentially cytotoxic materials. Khaw et al., xe2x80x9cFive-minute Treatments with Fluorouracil, Floxuridine, and Mitomycin Have Long-term Effects on Human Tenon""s Capsule Fibroblastsxe2x80x9d, Arch. Ophthalmol., 110:1150-54 (1992).
Similar effects have been noted with mitomycin or mitomycin C (xe2x80x9cMMCxe2x80x9d). Because it is much more potent than 5-FU, MMC can also be administered in a single intraoperative application, typically with a contact time of about one to five minutes, followed by copious irrigation. MMC is an alkylating antiproliferative agent isolated from the fermentation filtrate of a particular species of Streptomyces. It is an anti-fibrotic, anti-neoplastic antibiotic that prevents the scarring of filtration blebs by inhibiting the proliferation of fibroblasts. It is usually effective in reducing postoperative subconjunctival fibrosis and, thus, tends to lengthen the survival time of filtration blebs and to reduce the IOP.
However, MMC is also cytocidal at high concentrations and produces undesirable ocular hypotony (IOP less than 5 or 6 mm Hg) in as much as ⅓ of the patients treated with it. Other undesirable side effects include conjunctival wound leaks, choroidal detachments, and hypotony maculopathy, with a probability of late-onset bleb leaks of around 25% See Khaw et al., xe2x80x9cFive-minute Treatments with Fluorouracil, Floxuridine, and Mitomycin Have Long-term Effects on Human Tenon""s Capsule Fibroblastsxe2x80x9d, Arch. Ophthalmol., 110:1150-54 (1992); Zacharia et al., xe2x80x9cOcular Hypotony after Trabeculectomy with Mitomycin Cxe2x80x9d, Am. J. of Ophthalmology, 116:314-26 (1993); Kupin et al., xe2x80x9cAdjunctive Mitomycin C in Primary Trabeculectomy in Phakic Eyesxe2x80x9d, Am. J. of Ophthalmology, 119:30-39 (1995); Katz et al., xe2x80x9cMitomycin C versus 5-Fluorouracil in High-risk Glaucoma Filtering Surgeryxe2x80x9d, Ophthalmology, 102:9, 1263-69 (1995); Shin et al., xe2x80x9cAdjunctive Subconjunctival Mitomycin C in Glaucoma Triple Procedurexe2x80x9d, Ophthalmology, 102:10, 1550-58 (1995); Nouri-Mahdavi et al., xe2x80x9cOutcomes of Trabeculectomy for Primary Open-angle Glaucomaxe2x80x9d, Ophthalmology, 102:12, 1760-69 (1995); and Mora et al., xe2x80x9cTrabeculectomy with Intraoperative Sponge 5-Fluorouracilxe2x80x9d, Ophthalmology, 103:963-970 (1996). One group of investigators even reported an increased incidence of scleritis, involving severe pain and redness of the sclera, following topical treatment with MMC during trabeculectomy. Fourman, xe2x80x9cScleritis after Glaucoma Filtering Surgery with mitomycin Cxe2x80x9d, Ophthalmology, 102:10, 1569-71(1995). See also Liang et al. xe2x80x9cComparison of Mitomycin C and 5-Fluorouracil on Filtration Surgery Success in Rabbit Eyesxe2x80x9d, J. Glaucoma, 1:87-93 (1992).
Other scientists have reported the use of laser sclerostomy along with either 5-FU or MMC. While the use of 5-FU administered after laser treatment over a two-week period was described as successful by Berlin et al., xe2x80x9cThe Role of Laser Sclerostomy in Glaucoma Surgeryxe2x80x9d, Current Opinion in Ophthalmology, 6:11, 102-114 (1995), it was suggested that the use of MMC administered by a number of different channels (subconjunctival injection, subconjunctival gel foam, topical drops or by absorbent sponges), along with laser treatment, could be even more effective. However, the usual complications were also noted, i.e., corneal toxicity, wound leak, chronic hypotony, choroidal detachment, and hyotonous maculopathy.
Beta-aminopropionitrite (xe2x80x9cBAPNxe2x80x9d) and D-penicillamine have been used to inhibit the cross-linking of collagen fibers, which may help to keep collagen in an immature state after filtration surgery and, consequently, limit bleb scarring. An initial report using topical BAPN ointment postoperatively found that it kept the IOP below 22 mm Hg in 74% of the patients. However, animal studies using both BAPN and D-penicillamine showed only limited potency. Stewart, xe2x80x9cFiltering Surgeryxe2x80x94Techniques and Operative Complicationsxe2x80x9d, Clinical Practice of Glaucoma, Chapter 10, 333-61 (1990).
For a discussion of bleomycin, see Khaw et al., xe2x80x9cEffects of Inoperative 5-Fluorouracil or Mitomycin C on Glaucoma Filtration Surgery in the Rabbitxe2x80x9d, Ophthalmology, 100:367-72 (1993). For a discussion of cytosine arabinocide-impregnated polymers, see Lee et al., xe2x80x9cEffects of Cytosine Arabinoside-impregnated Bioerodible Polymers on Glaucoma Filtration Surgery in Rabbitsxe2x80x9d, J. Glaucoma, 2:96-100 (1993).
Photodynamic therapy (xe2x80x9cPDTxe2x80x9d) is known as an approved cancer treatment that can be used for many purposes, such as the treatment of solid tumors (e.g., U.S. Pat. Nos. 4,932,934 and 5,283,255); the impairment of blood-borne targets such as leukemic cells, immunoreactive cells (copending application Ser. Nos. 07/889,707; 08/309,509, 08/374,158 and 08/174,211), and unwanted microorganisms (U.S. Pat. No. 5,360,734); the prevention of restenosis (U.S. Pat. No. 5,422,362); the diagnosis and treatment of certain neovascular ocular disorders (co-pending application Ser. Nos. 08/209,473, 08/390,591 and 08/613,420); the removal of atherosclerotic plaque (co-pending application Ser. No. 08/663,890); and the prevention of transplant rejection (co-pending application Ser. No. 08/371,707).
PDT involves the local or systemic application of a light-absorbing photosensitive agent, usually a porphyrin derivative, which accumulates selectively in target tissues. Upon irradiation with visible light of an activating wavelength, reactive oxygen species are produced in cells containing the photosensitizer, which promote cell death. For example, in the treatment of tumors, the photosensitization process is thought to give rise to singlet oxygen, an activated derivative of molecular oxygen, which may oxidatively react with a number of specific sites in cells and tissues. As a consequence, the tumor cells undergo irreversible damage at a subcellular levels, especially in the cell membrane and mitochondria. In vivo, tumor destruction is the result of a complex interplay of multiple factors affecting the framework of connective tissue that physically supports the stroma of a tumor and the vascular tissue that nourishes the tumor. Zhou, xe2x80x9cMechanisms of Tumor Necrosis Induced by Photodynamic Therapyxe2x80x9d, J. of Photochem. and Photobiol., B: Biology, 3, 299-318 (1989).
It is clear that photosensitizers are preferentially taken up and accumulate in tumor tissue and that some tumor stroma cell necrosis is selectively and directly caused by PDT. However, vascular injury and the subsequent anoxia of tumor cells are also involved in the tumor necrotizing process induced by PDT. Particularly in this latter event, PDT-induced tumor necrosis has been considered the result of an acute inflammatory reaction to the physicochemical changes in the vascular wall. The rapid reduction in blood supply, as well as the onset of inflammatory edema in the tumor, leads to hypoxia or even anoxia of the photoinjured neoplastic cells, which eventually undergo necrosis. The overall damaging process is multiplied by the release of vasoactive or tissue-lysing substances such as histamine, proteases and acid phosphatases from photodamaged mast cells and neutrophils in the tumor stroma, which are also associated with inflammatory processes. Zhou, xe2x80x9cMechanisms of Tumor Necrosis Induced by Photodynamic Therapyxe2x80x9d, J. of Photochem. and Photobiol., B: Biology, 3, 299-318 (1989).
It has been recognized that the acute inflammatory phase usually induced by PDT in approved cancer treating protocols is a double-edged sword. The study of experimental tumor models has shown that, after PDT is administered, a protein- and neutral lipid-rich exudate infiltrates into the extracellular space and accumulates against a xe2x80x9cwallxe2x80x9d of perinecrotic vital cells (xe2x80x9chypoxic cellsxe2x80x9d), which are stuck against the xe2x80x9cghostsxe2x80x9d of necrotic cells. From a positive cancer treatment perspective, the inflammatory exudate may help to deliver protein-bound photosensitizers to the inner areas of the tumor that would otherwise be difficult to reach. On the other hand, this flow of inflammatory exudate may also bring oxygen and nutrients and thus help to nourish cells engaged in wound repair processes. Therefore, the occurrence of an inflammatory state associated with PDT has been recognized a fact of life that often complicates the treatment of cancerous tumors. Freitas, xe2x80x9cInflammation and Photodynamic Therapyxe2x80x9d, J. Photochem. and Photobiol., B: Biology, 8: 340-41 (1991).
Some work has been done with PDT to achieve an antifibrosis effect in connection with glaucoma filtering surgery using tin ethyl etiopurpurin (xe2x80x9cSnET2xe2x80x9d) as the photosensitive agent. Specifically, rabbits that received subconjunctival injections of SnET2 underwent filtering surgery followed by post-operative light irradiation. Hill et al., xe2x80x9cPhotodynamic Therapy with Tin Ethyl Etiopurpurin as an Alternative Anti-fribrotic Treatment Following Glaucoma Filtering Surgeryxe2x80x9d, Photochem. Photobiol, 61 Suppl., 68S, TPM-E9 (1995); and Hill et al., xe2x80x9cPhotodynamic Therapy (PDT) for Antifibrosis in a Rabbit Model of Filtration Surgeryxe2x80x9d, Investigative Ophthalmology and Visual Science, 36:4, S877 (1995). However, in this preliminary work, the authors do not report any control data and, therefore, it is difficult to determine how much the Hill et al. treatment actually prolonged the survival of the filtration bleb over untreated blebs.
Further, Hill et al. disclose that more than three hours elapsed after the injection of the photosensitive agent before the surgery and the irradiation step took place, which would have allowed sufficient time for the photosensitizer to be absorbed by the tissues associated with injury, but would also have allowed the photosensitizing agent to spread to other non-target areas of the eye. Because the authors report that large, transient areas of avascular conjunctiva were produced, with the avascular region not being limited to the filtration bleb until a full four weeks after the surgery, it is clear that undesirably large areas of the eye were affected by the treatment. In view of the well-known potentially destructive, necrotic effect of PDT in other applications, there is a need for the reduction or prevention of inflammation in such a way that the degree and extent of pharmacological activity can be reliably controlled.
Surprisingly, it has now been found that, with the appropriate choice of a photosensitizing agent that is rapidly absorbed by injured tissues, but non-toxic in the absence of light, PDT can have a predictable and beneficial anti-inflammatory effect that is useful even for delicate tissues, such as the eye area. This is a particularly surprising discovery in view of teachings in the past that PDT has been responsible for actually causing inflammatory responses, rather than having the ability to reduce or prevent them.
Specifically, it has now been discovered that the effects of inflammation arising from injured tissue can be reduced or prevented by low-dose PDT. Specifically, the method of the invention for reducing or preventing such inflammation comprises the steps of:
a. bringing the injured tissue, or pre-injured tissue, into contact with a photosensitizing agent capable of penetrating into the tissue, resulting in the desired degree of biodistribution in less than one hour; and
b. exposing the tissue thus brought into contact to light having a wavelength absorbed by the photosensitizing agent for a time sufficient to reduce or prevent inflammation in the exposed tissue, but not so long as to cause necrosis or-erythema of the exposed tissue.
The method of the invention is particularly advantageous when the injured tissue is highly sensitive to further injury or inflammation, such as in ocular tissue, because appropriate photosensitizers are not, in themselves, antiproliferative in effect or cytotoxic to delicate tissues in the absence of activating irradiation. Further, because most photosensitizing agents are non-toxic to human tissue unless activated by light and because the photosensitizing agent of the invention is capable of penetrating into injured tissue relatively quickly, the degree of pharmacologic activity is easily controlled both by the extent of the irradiation and either the extent of physical contact with the photosensitizer or its concentration, e.g., in the bloodstream, at the time of irradiation. Consequently, the therapeutic effect of the invention is more easily regulated than known pharmacologic anti-fibrotic techniques.
In another embodiment, the invention relates to a composition for reducing or preventing the effects of inflammation arising from injured tissue comprising:
a. from about 1 xcexcg/mL to about 2 mg/mL of a photosensitizing agent capable of penetrating into the injured tissue, or pre-injured tissue, resulting in the desired degree of biodistribution in less than about one hour and;
b. a pharmaceutically acceptable carrier.
In yet another embodiment, the invention relates to an article for reducing or preventing the effects of inflammation arising from injured tissue, which article comprises:
a. a photosensitizing agent capable of penetrating into the injured tissue, or pre-injured tissue, resulting in the desired degree of biodistribution in less than one hour; and
b. an absorbent applicator.